Gitlab.io page with let's encrypt: Handshake Error for IE11 on Win7/8

Hi

I have a site running on gitlab pages, using Let’s Encrypt (default config via gitlab), which works fine except on IE11 on Win7/8. Site is https://klimaliste-erlangen.de

SSL Test see: https://www.ssllabs.com/ssltest/analyze.html?d=klimaliste-erlangen.de&hideResults=on

Is there anything I can do to get it working on IE11/Win7? As this is a public website, I cannot tell users to upgrade or use a real browser…

Thanks!
Nils